This invention relates to a fastener and, in particular, a pressure-indicating fastener capable of providing a visual indication of a pressure threshold applied to the fastener.
In the past, there have been many different types of fastening devices used to join at least two different elements. Typically, these fastening devices involve the application of pressure to accomplish the fastening. By way of example, a non-exhaustive list of such devices include clamps, crimp rings, nut-and-bolt combinations, rivets, screws, straps, etc.
Typically, installation of such fastening devices requires a minimum application of pressure to ensure that fastening has been properly effected. In some applications, special tools, such as a torque wrench in the installation of a nut-and-bolt fastener, are used to indicate the amount of force applied to the fastener. In the instance of the torque wrench, other than the applied pressure being indicated by the torque wrench, there is no positive indication that the nut and bolt are installed with the correct pressure. Further, a visual inspection of the installed fastener would not reveal improper installation.
In another situation, when large plumbing systems are installed, there may be dozens of crimp rings that are applied to tube/fitting assemblies that are assembled prior to a contractor crimping the various assemblies. The contractor might forget to crimp a ring and an inspector may not catch the missed crimp ring. If the construction proceeds, the assembly may prematurely fail and cause damage to the completed unit. For example, long after an improperly installed piping joint has been covered up, it could involve considerable additional expense to repair given the difficulty of accessing the joint. Consequently, it is important that there be an easy and reliable indicator of the fact that the crimp ring has been or has not been properly crimped.
Accordingly, it is an object of this invention to at least partially overcome the disadvantages of the prior art. Thus, it is an object of this invention to provide an improved type of fastener which is capable of providing a visual indication of a pressure threshold applied to the fastener.
Accordingly, in one of its aspects, this invention resides in a fastener comprising a fastening portion which is actuated to fasten by way of application of a sufficient actuating pressure on an actuating surface of the fastening portion; and a pressure-sensitive substance associated with at least part of the actuating surface such that the actuating surface visibly changes colour after the sufficient actuating pressure is applied to the actuating surface.